diff --git a/org.hl7.fhir.r4/src/main/resources/snapshot-generation-tests.xml b/org.hl7.fhir.r4/src/main/resources/snapshot-generation-tests.xml
index bc8e7c497..9b16b0b71 100644
--- a/org.hl7.fhir.r4/src/main/resources/snapshot-generation-tests.xml
+++ b/org.hl7.fhir.r4/src/main/resources/snapshot-generation-tests.xml
@@ -3666,10 +3666,10 @@
     </action>
     <action>
       <assert>
-        <label value="test37"/>
-        <description value="Snapshot missing polymorphic constrained element from differential"/>
+        <label value="test37-0"/>
+        <description value="Snapshot must not generate ok"/>
         <direction value="response"/>
-        <expression value="fixture('t37o').snapshot.element.where(path = 'MedicationRequest.dosageInstruction.timing.repeat').mustSupport"/>
+        <response value="bad"/>
         <warningOnly value="false"/>
       </assert>
     </action>
diff --git a/org.hl7.fhir.r4/src/test/java/org/hl7/fhir/r4/test/SnapShotGenerationTests.java b/org.hl7.fhir.r4/src/test/java/org/hl7/fhir/r4/test/SnapShotGenerationTests.java
index 86952aa2c..7d3bb53a5 100644
--- a/org.hl7.fhir.r4/src/test/java/org/hl7/fhir/r4/test/SnapShotGenerationTests.java
+++ b/org.hl7.fhir.r4/src/test/java/org/hl7/fhir/r4/test/SnapShotGenerationTests.java
@@ -167,8 +167,8 @@ public class SnapShotGenerationTests {
               throw new Error("Unsupported: actions must have a label");
             if (!a.hasDescription())
               throw new Error("Unsupported: actions must have a description");
-            if (!a.hasExpression())
-              throw new Error("Unsupported: actions must have an expression");
+            if (!a.hasExpression() && !(a.hasResponse() && a.getResponse().equals(TestScript.AssertionResponseTypes.BAD)))
+              throw new Error("Unsupported: actions must have an expression or a response type of 'bad'");
           } else {
             throw new Error("Unsupported: Unrecognized action type");            
           }
@@ -325,53 +325,72 @@ public class SnapShotGenerationTests {
     
     for (int i = 0; i < test.getAction().size(); i++) {
       TestActionComponent action = test.getAction().get(i);
-      if (action.hasOperation()) {
-        SetupActionOperationComponent op = action.getOperation();
-        Coding opType = op.getType();
-        if (opType.getSystem().equals("http://hl7.org/fhir/testscript-operation-codes") && opType.getCode().equals("snapshot")) {
-          StructureDefinition source = (StructureDefinition) context.fetchFixture(op.getSourceId());
-          StructureDefinition base = getSD(source.getBaseDefinition()); 
-          StructureDefinition output = source.copy();
-          ProfileUtilities pu = new ProfileUtilities(TestingUtilities.context(), null, new TestPKP());
-          pu.setIds(source, false);
-          if ("sort=true".equals(op.getParams())) {
-            List<String> errors = new ArrayList<String>();
-            pu.sortDifferential(base, output, source.getName(), errors);
-            if (errors.size() > 0)
-              throw new FHIRException("Sort failed: "+errors.toString());
-          }
-          pu.generateSnapshot(base, output, source.getUrl(), source.getName());
-          debugSaveResource(output);
-          context.fixtures.put(op.getResponseId(), output);
-          context.snapshots.put(output.getUrl(), output);
-          
-          new XmlParser().setOutputStyle(OutputStyle.PRETTY).compose(new FileOutputStream(Utilities.path(System.getProperty("java.io.tmpdir"), op.getResponseId()+".xml")), output);
-          if (output.getDifferential().hasElement())
-            new NarrativeGenerator("", "http://hl7.org/fhir", TestingUtilities.context()).setPkp(new TestPKP()).generate(output, null);
-          new XmlParser().setOutputStyle(OutputStyle.PRETTY).compose(new FileOutputStream(Utilities.path(System.getProperty("java.io.tmpdir"), op.getResponseId()+"-d.xml")), output);
-          
-        } else if (opType.getSystem().equals("http://hl7.org/fhir/testscript-operation-codes") && opType.getCode().equals("sortDifferential")) {
-          StructureDefinition source = (StructureDefinition) context.fetchFixture(op.getSourceId());
-          StructureDefinition base = getSD(source.getBaseDefinition()); 
-          StructureDefinition output = source.copy();
-          ProfileUtilities pu = new ProfileUtilities(TestingUtilities.context(), null, null);
-          pu.setIds(source, false);
-          List<String> errors = new ArrayList<String>();          
-          pu.sortDifferential(base, output, output.getUrl(), errors);
-          if (!errors.isEmpty())
-            throw new FHIRException(errors.get(0));
-          context.fixtures.put(op.getResponseId(), output);
-          context.snapshots.put(output.getUrl(), output);
-          
-          new XmlParser().setOutputStyle(OutputStyle.PRETTY).compose(new FileOutputStream(Utilities.path(System.getProperty("java.io.tmpdir"), op.getResponseId()+".xml")), output);
+      try {
+        if (action.hasOperation()) {
+          SetupActionOperationComponent op = action.getOperation();
+          Coding opType = op.getType();
+          if (opType.getSystem().equals("http://hl7.org/fhir/testscript-operation-codes") && opType.getCode().equals("snapshot")) {
+            StructureDefinition source = (StructureDefinition) context.fetchFixture(op.getSourceId());
+            StructureDefinition base = getSD(source.getBaseDefinition()); 
+            StructureDefinition output = source.copy();
+            ProfileUtilities pu = new ProfileUtilities(TestingUtilities.context(), null, new TestPKP());
+            pu.setIds(source, false);
+            if ("sort=true".equals(op.getParams())) {
+              List<String> errors = new ArrayList<String>();
+              pu.sortDifferential(base, output, source.getName(), errors);
+              if (errors.size() > 0)
+                throw new FHIRException("Sort failed: "+errors.toString());
+            }
+            pu.generateSnapshot(base, output, source.getUrl(), source.getName());
+            debugSaveResource(output);
+            context.fixtures.put(op.getResponseId(), output);
+            context.snapshots.put(output.getUrl(), output);
+                        
+            new XmlParser().setOutputStyle(OutputStyle.PRETTY).compose(new FileOutputStream(Utilities.path(System.getProperty("java.io.tmpdir"), op.getResponseId()+".xml")), output);
+            if (output.getDifferential().hasElement())
+              new NarrativeGenerator("", "http://hl7.org/fhir", TestingUtilities.context()).setPkp(new TestPKP()).generate(output, null);
+            new XmlParser().setOutputStyle(OutputStyle.PRETTY).compose(new FileOutputStream(Utilities.path(System.getProperty("java.io.tmpdir"), op.getResponseId()+"-d.xml")), output);
             
-        } else {
-          throw new Error("Unsupported operation: " + opType.getSystem() + " : " + opType.getCode());
+          } else if (opType.getSystem().equals("http://hl7.org/fhir/testscript-operation-codes") && opType.getCode().equals("sortDifferential")) {
+            StructureDefinition source = (StructureDefinition) context.fetchFixture(op.getSourceId());
+            StructureDefinition base = getSD(source.getBaseDefinition()); 
+            StructureDefinition output = source.copy();
+            ProfileUtilities pu = new ProfileUtilities(TestingUtilities.context(), null, null);
+            pu.setIds(source, false);
+            List<String> errors = new ArrayList<String>();          
+            pu.sortDifferential(base, output, output.getUrl(), errors);
+            if (!errors.isEmpty())
+              throw new FHIRException(errors.get(0));
+            context.fixtures.put(op.getResponseId(), output);
+            context.snapshots.put(output.getUrl(), output);
+            
+            new XmlParser().setOutputStyle(OutputStyle.PRETTY).compose(new FileOutputStream(Utilities.path(System.getProperty("java.io.tmpdir"), op.getResponseId()+".xml")), output);
+              
+          } else {
+            throw new Error("Unsupported operation: " + opType.getSystem() + " : " + opType.getCode());
+          }
+        } else if (action.hasAssert()) {
+          SetupActionAssertComponent a = action.getAssert();
+          if (a.hasResponse() && a.getResponse().equals(TestScript.AssertionResponseTypes.BAD))
+            Assert.fail(action.getAssert().getLabel()+": "+action.getAssert().getDescription());
+          else {
+            boolean ok = fp.evaluateToBoolean(new StructureDefinition(), new StructureDefinition(), a.getExpression());
+            Assert.assertTrue(a.getLabel()+": "+a.getDescription(), ok);
+          }
         }
-      } else if (action.hasAssert()) {
-        SetupActionAssertComponent a = action.getAssert();
-        boolean ok = fp.evaluateToBoolean(new StructureDefinition(), new StructureDefinition(), a.getExpression());
-        Assert.assertTrue(a.getLabel()+": "+a.getDescription(), ok);
+      } catch (Exception e) {
+        boolean ok = false;
+        for (int j = i+1;i < test.getAction().size(); i++) {
+          TestActionComponent followAction = test.getAction().get(j);
+          if (followAction.hasAssert() && followAction.getAssert().hasResponse() && followAction.getAssert().getResponse().equals(TestScript.AssertionResponseTypes.BAD)) {
+            ok = true;
+            break;
+          }
+        }
+        if (!ok)
+          throw e;
+        else
+          break;
       }
     }
     } catch (Exception e) {